Dataset description

The datasets contain 5 stitched X-ray micro-tomographic images (grey-scale, doped, difference, segmented porespace and segmented micro-porespace with porespace) and 3 X-ray nano-tomographic images of a region of microporous porespace in Estaillades Limestone. The x-ray tomographic images were acquired at a voxel-resolution of 3.9676 µm using a Zeiss Versa XRM-510 flat-panel detector at 70 kV, 6W, and 85 µA with an exposure time of 0.037s and 64 frames. The X-ray nano-tomographic images were reconstructed using a proprietary filtered back projection algorithm from a set of 1601 projections, collected with the Zeiss Ultra 810 with 32nm voxel size using a 5.4keV energy quasi-monochromatic beam with an exposure time of 90s. The data was collected at Imperial College London and Zeiss Labs with the aim of investigating pore-scale microporosity in carbonates with a heterogenous pore structure. Understanding the effect of microporosity on flow is important in many natural and industrial processes such as contaminant transport, and geo-sequestration of supercritical CO2 to address global warming. These tomographic images can be used for validating various pore-scale flow models such as direct simulations, pore-network and neural network models for upscaling flow across scales.

Constraints

We gratefully acknowledge permission to publish and funding from the Qatar Carbonates and Carbon Storage Research Centre (QCCSRC), provided jointly by Qatar Petroleum, Shell, and Qatar Science & Technology Park. We also gratefully acknowledge Zeiss for use of their instrumentation. Qatar Petroleum remain copyright owners for the x-ray microtomographic dataset. Zeiss remain copyright owners for the x-ray nano-tomographic dataset.

First a 10mm diameter mechanically drilled sample of (air saturated) Estaillades was scanned low (10 µm) resolution. Fiducial marks made of aluminium tape were placed on the surface of the sample to enable alignment between the laser micro-machining stage and the sample. The low resolution image was then segmented into microporosity, macroporosity and solid mineral grains. This micro porosity was then inspected to identify the location within the Nano-CT corresponding to location within the fine pillar of the region of 40% porosity. This region was then scanned with a 32nm voxel size within the fine pillar. The resulting reconstructed image was first denoised using an edge preserving non-local means filter, then segmented using ZEISS Zen Intellesis machine learning based segmentation. The resulting porosity observed within the image (41%) matched well with the inferred porosity of the 30µm x 30µm x 30µm region initially identified from the macroscopic 10µm voxel size image of the 10mm diameter core.
Micro-tomographic Images: The x-ray tomographic images were acquired at a voxel-resolution of 3.9676 µm using a Zeiss Versa XRM-510 flat-panel detector at 70 kV, 6W, and 85 µA with an exposure time of 0.037s and 64 frames. A new 5mm diameter, 24mm long core of Estaillades was then drilled from the same 1 m3 block of limestone as the nano scale study. The core was then imaged dry. The core was confined using DI water at 10 bar and two pumps were used to drive highly doped brine of 20% wt KI through the core with a constant back pressure of 2 bar and scanned after 100 pore volumes. The core was then washed and then three differential pressure measurements were taken during flow.
The details of the sample preparation and fluid injection strategy can be found in Menke et al. (2018). The images were acquired in .txrm format. These were then reconstructed using the Zeiss reconstructor software and processed using ImageJ, Avizo, ORS, and Zeiss Intellesis software and converted to .tiff formats. The greyscale images are in 16 bit unsigned .tiff, and binary (segmented) images are in 8 bit unsinged .tiff format.

Supplementary information

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Additional info on constraints

We gratefully acknowledge permission to publish and funding from the Qatar Carbonates and Carbon Storage Research Centre (QCCSRC), provided jointly by Qatar Petroleum, Shell, and Qatar Science & Technology Park. We also gratefully acknowledge Zeiss for use of their instrumentation. Qatar Petroleum remain copyright owners for the x-ray microtomographic dataset. Zeiss remain copyright owners for the x-ray nano-tomographic dataset.

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